That was followed by a prison consultant's testimony that such incidents are difficult to prevent, in part because the prison is badly understaffed.

That prison expert, Dr. Jeffrey Schwartz, called the Orleans Parish Prison, "One of the worst jails in America."

The former OPP inmate who was called to the witness stand Monday, said the attack took place over several hours one night in a section of a prison dormitory. He claimed several other inmates tied him up, beat him with a mop and violently raped him and he often "feared for his life".

Monday's testimony came during a hearing on a proposed agreement between Sheriff Marlin Gusman, who operates the jail, and the U.S. Justice Department on improving jail conditions.

The city of New Orleans, which funds the jail, is opposing the agreement, saying its cost could force cutbacks in police and other vital services.

Mayor Mitch Landrieu says city expenses required under the agreement could run into many millions of dollars.

He told the City Council last week that the sheriff's agreement could drain the city of funds it needs to provide basic services while fulfilling its own commitment to reform the New Orleans Police Department.